1. Field of the Invention
The invention relates generally to vehicle simulation and, more particularly, to a seat for inducing motion sensations similar to those experienced during actual operation of a vehicle. The invention is particularly useful in providing sustained acceleration cues and enhancing motion onset cues in an aircraft simulator.
2. Description of the State of the Art
Man's sensory systems provide the interface between him and his environment; through these systems travels the raw information used in learning and the maintenance of task proficiency. Aircraft simulation, a technique employed primarily for pilot training, naturally depends heavily on the role sensory systems play in this learning process. It has long been hypothesized in the simulator art that kinesthetic feedback from a pilot's sensory systems is important in mastering the piloting task.
Man is thought to perceive motion through at least three basic sensory systems; they are visual, vestibular and haptic systems. A detailed description of the role played by these sensory systems in kinesthetic determination may be found in a paper by G. J. Kron entitiled "Motion Simulation Enhancement: the Development of a Research G-Seat System" printed at pages 14 - 54 in Proceedings of the Sixth Naval Training Equipment Center And Industry Conference, published Nov. 13, 1973, as NAVTRAEQUIPCENIH-226 report, which paper is incorporated by reference herein.
As pointed out in the referenced paper, the vestibular system, located in the inner ear, is the best known motion sensory system. The organs of this system not only detect body movement and gravity vector orientation, but also contribute to the sense of balance and orientation.
The haptic system, a lesser known and far from formalized system, deals in part with the perception known as "body feel." The elements of the haptic sensory system are employed in perceiving physiological changes which occur when an individual is subjected to motion variations. Most of these changes manifest themselves in one or more of four modalities: skeletal attitude changes, muscle tonal changes, pressure gradient changes, and touch or area of contact changes.
Consider, by way of example, physiological changes detected by the haptic system during an aircraft dive-pullout maneuver. In this sustained acceleration situation, the pilot is subjected to a "g" loading or increase in apparent body weight, proportional to the number of g's of acceleration experienced by the aircraft. Assuming the pilot is seated, one would expect his head, neck and upper torso to compress along the spinal axis, his shoulders to droop under the "added" weight of his upper arms, and his buttocks to sink deeper into the seat cushion, thereby decreasing the included angle between upper and lower portions of the legs. In other words, his body orientation will change slightly due to the increase in apparent weight. Further, one would expect the pilot's flesh to droop and thereby change the loading characteristics of his muscles. As the inertial weight of the pilot's torso increases, the pressure gradient over his buttocks will change as the primary bone structure in this region, the ischial tuberosities, transmit loading to the surface of the seat. The flesh trapped between the ischial tuberosities and the seat is subjected to increased pressure and the resultant change in pressure gradient in this area of the buttocks is detected by haptic system pressure-sensitive receptors. Finally, under increased g loading, the pilot settles deeper into the seat bringing a larger portion of his buttocks and thigh flesh area into contact with the seat. Receptor units allied with a sense of cutaneous touch would thus indicate that more of the seat is touching the pilot's flesh. From this example, it should be apparent that the combined response of the haptic system elements provides a fairly sophisticated definition of body position and motion.
In present day aircraft simulators, a simulated cockpit is supported on a motion base. The motion base or system is designed to reposition the simulated cockpit and is primarily directed towards influencing a pilot trainee's vestibular system. Until now, little overt effort has been aimed directly at the haptic system channels. The present invention thus represents a major departure from the prior art in that it is designed strictly for haptic system excitation.
Motion bases, owing to their mechanical constraints, produce the most useful stimuli, or "cues," during the onset phase of low-level, short-term accelerations. However, as the accelerations become larger in magnitude and longer in duration, the limits of the motion system are approached and cue generation constrained or terminated. The G seat of the instant invention is designed to provide a sustained acceleration cue as well as to complement the onset acceleration cue that is provided by the motion base.
A number of prior art devices have attempted to induce acceleration sensations by body manipulation. See, for example, U.S. Pat. Nos. 3,097,346; 3,270,440 and 3,309,795. These prior art devices fall into two categories of design: seats constructed of soft pliable bladders, and seats constructed of upholstered movable plates. The former are driven pneumatically and the latter through linkages by drive actuators.
A basic shortcoming of both of these former designs is the relatively small number of driven elements comprising the seat. The instant inventors have discovered that it is desirable necessary to use a mosaic of many elements in order to provide seat movement suitable to the various elements of the haptic sensory system. Further, it is required that each of these mosaic elements have an excursion range suitable to permit the composite of all mosaics to form plane changes in attitude, elevation and shape. In the prior art upholstered movable plate design, the linkage arrangement is discordant with a mosaic approach wherein each mosaic element must be small, yet have substantial excursion range.
A major detraction of the soft pliable bladder approach is the fact that conflicting stimuli are produced. Consider, again, the aircraft drive pullout situation. In order to cause a subject to settle in a seat composed of air bladders, the air pressure in the bladders is reduced, resulting in the desired skeletal attitude change. However, the air cells or bladders change shape under the pressure reduction and become more pliable and, consequently, fit the natural form of the buttocks more precisely, thereby reducing the buttocks flesh pressure gradient. As mentioned earlier, an increased flesh pressure graident, not decreased gradient, is desired under this acceleration condition. Equally as undesirable is the very turgid surface presented when the bladders attempt to shift the body upwards under footwards acceleration conditions.
Further complicating the soft bladders approach is the fact that its only loading is afforded by the body weight it supports. In attempting to provide a new elevation for the bladders, internal pressure of the bladders is altered and the body shifted until the new load "seen" by the bladders compensates for the pressure change. Such conditions permit the bladders to either completely collapse or completely distend if enough body load cannot be shifted between adjacent bladders. Seat cushion ballooning results. Although the problem can be minimized by shifting to a pneumatic drive based on controlling air mass (volume) rather than pressure, the conflicting stimuli problem will remain inherent in the pliable bladders.
Another shortcoming of the prior art seats is that they often require unusual straps or harnasses to control the movement of the subject's body and thus fail to maintain cockpit fidelity.